1. Field of the Invention
The present invention generally relates to an image synthesizing apparatus and method, for combining two images encoded according to the JPEG-2000 Standard, for example, and more particularly to an image synthesizing apparatus and method suitable for use in the cross fading.
This application claims the priority of the Japanese Patent Application No. 2003-120367 filed on Apr. 24, 2003, the entirety of which is incorporated by reference herein.
2. Description of the Related Art
Conventionally, the cross fading is well-known as an image processing technique for representing a transition from one image as a whole to another, for example (cf. Japanese Published Unexamined Patent Application Nos. 2000-78467 and -184278). The cross-fading technique is used in the computer graphics, special playback in a broadcast equipment, special playback in a camcorder, image processing in a game machine, etc.
Normally, the cross fading is implemented by linearly interpolating pixels included in two different images and taking spatially corresponding positions in the images, respectively, and combining the two images together.
Recently, more and more researches have been done of the techniques of dividing an image into a plurality of frequency bands by a so-called filter bank including a high-pass filter and low-pass filter in combination to encode each of the frequency bands. Of such techniques, the wavelet transform coding is considered as a new promising technique which will take the place of DCT (discrete cosine transform) because a high compression results in no considerable block distortion as in the DCT. For example, the JPEG-2000 Standard established as an international standard in January, 2001 has attained a greater improvement in efficiency of coding than the conventional JPEG by adopting a combination of the wavelet transform and a high-efficiency entropy coding (bit modeling and arithmetic coding, both in units of a bit plane).
Note here that to form an encoded code stream of a cross-faded image from an encoded code stream of each of two images with the use of the above-mentioned conventional technique, it is necessary to decode the encoded code streams according to the JPEG-2000 Standard, combine the two decoded images thus acquired by the linear interpolation to generate a cross-faded image, and encode the cross-faded image according to the JPEG-2000 Standard.
However, such a technique requires a memory for storing the two decoded images and also a memory for storing the cross-faded image. In addition, it needs both an image decoder and image encoder, which comply with the JPEG-2000 Standard.